Recently, according to the requirement of low fuel consumption in an automobile, a conjugated diene polymer having a small rolling resistance, good abrasion resistance and tensile properties, and vehicle stability which is represented by wet skid resistance is required as a rubber material for a tire.
In order to decrease the rolling resistance of the tire, a method of decreasing the hysteresis loss of vulcanized rubber is suggested. As the evaluation index of the vulcanized rubber, repulsive elasticity at 50° C. to 80° C., tan δ, Goodrich heating, etc. are used. That is, a rubber material having large repulsive elasticity or small tan δ or Goodrich heating is preferably used.
As a rubber material having small hysteresis loss, natural rubber, polyisoprene rubber, polybutadiene rubber, etc., are known, however these materials have small wet skid resistance. Recently, a conjugated diene (co)polymer such as styrene-butadiene rubber (hereinafter, will be referred to as SBR) and butadiene rubber (hereinafter, will be referred to as BR) is prepared by an emulsion polymerization or a solution polymerization, and used as rubber for a tire. The strongest points of the solution polymerization with respect to the emulsion polymerization includes that the amount of a vinyl structure and the amount of styrene regulating the physical properties of the rubber may be optionally controlled, and the molecular weight and the physical properties may be controlled via coupling, modification, etc. Therefore, the structure of the SBR or BR rubber finally produced may be easily change, the movement of the terminal of a chain may decrease due to the bonding or modification of the terminal of a chain, and the bonding force with a filler such as silica and carbon black may increase. Accordingly, the SBR rubber by the solution polymerization may be widely used as a rubber material for a tire.
In the case that such SBR obtained by the solution polymerization is used as the rubber material for a tire, the vinyl content in the SBR may increase, the glass transition temperature of the rubber may increase, physical properties required for the tire such as running resistance and breaking power may be controlled, and the glass transition temperature may be appropriately controlled, thereby reducing fuel consumption.
The SBR by the solution polymerization is prepared using an anion polymerization initiator, and is used after combining or modifying the terminal of the chain of the polymer thus formed using various modifiers.
Meanwhile, carbon black, silica, etc. are used as a filler for reinforcing a tire tread. In the case that the silica is used as the filler for reinforcing, low hysteresis loss and wet skid resistance may be improved. However, the silica with a hydrophilic surface with respect to carbon black with a hydrophobic surface has low affinity for rubber and inferior dispersibility, and a separate silane coupling agent is required to be used to improve dispersibility or impart bonding force between silica-rubber.
Accordingly, a method of introducing a functional group having affinity for or reactivity with silica at the terminal part of a rubber molecule is suggested, however effects thereof are insufficient.
In addition, in the case that the affinity only for the silica is increased, the affinity for the carbon black may be relatively deteriorated, and the application range thereof may be limited.
Accordingly, the development of rubber having high affinity for carbon black as well as silica is necessary.